1. Technical Field
The present invention relates to an electrode for a fuel cell, and to a membrane-electrode assembly and a fuel cell system that include the electrode.
2. Description of the Related Art
With rapid changes in electronic apparatus towards smaller products having greater functionality, a new field on which to focus research efforts is to meet the demands for higher efficiency and longer run time in power supply devices. Accordingly, the fuel cell, which converts chemical energy directly into electrical energy, is rising in importance as a new alternative method to increasing efficiency and run time.
The fuel cell is a power generation system which converts the chemical reaction energy of hydrogen and oxygen contained in hydrocarbon-based substances, such as methanol, ethanol, and natural gases, directly into electrical energy.
A fuel cell may be divided according to the type of electrolyte used, into a phosphoric acid fuel cell, molten carbonate fuel cell, solid oxide fuel cell, polymer electrolyte membrane fuel cell, or alkaline fuel cell. Although each of these fuel cells is operated by the same principle, each is different in terms of the type of fuel used, operating temperature, catalyst, and electrolyte, etc.
Among these, the polymer electrolyte membrane fuel cell (PEMFC) has superb output characteristics and low operating temperature, as well as fast activation and response characteristics. Thus, it has a wide range of applicability including not only movable power sources, such as those used in vehicles, but also distributed power sources, such as in houses and public buildings, and miniature power sources, such as for electronic apparatus.
In a fuel cell, hydrogen and fuel are supplied at the anode, while an oxidant is supplied at the cathode. Here, an oxidizing reaction of the hydrogen or fuel occurs at the anode, and a reduction reaction of the oxidant occurs at the cathode. The movement of electrodes thus created generates electricity, with heat and water generated as side products.
The generated water may have to be removed immediately through an outlet, because if the water is not removed, not only may the oxygen supply pressure gradually increase, but also the water content in the polymer electrolyte membrane inside the membrane-electrode assembly may be increased.
Thus, in order to discharge the water generated, a PEMFC or a direct methanol fuel cell (DMFC) employs a technique of forced pressure discharge using a blower. However, in forced pressure discharge, the efficiency may be decreased in inverse proportion to the size of the structure, because of the increased fluid resistance in microchannels or microstructures due to the relative increase in contact area between the fluid and the walls. Moreover, the force that can be created by a fan or blower mountable in a micro fuel cell may become significantly low compared to the capillary forces, when applied in a microstructure.
Therefore, research is needed on impact factors that maximize or minimize capillary forces which may induce abnormal flow, according to the operation requirements of miniature fuel cells, and there is a need for effectively discharging water produced in a fuel cell without using additional devices.